Percentage composition
Percentage composition is a Science & Technology concept from the MPSC syllabus, tested in 2 past MPSC questions (2015, 2023). Below are those real questions with their correct answers and explanations, plus the concepts worth being comfortable with first.
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Real questions that test this
खालीलपैकी कोणत्या हायड्रोकार्बनमध्ये 80% कार्बन असतो ? (H = 1, C = 12) Which of the following hydrocarbon has 80% carbon ? (H = 1, C = 12)
Percentage composition by mass = (mass of carbon / molar mass) x 100. Ethane (C2H6): molar mass = 2(12) + 6(1) = 30. %C = 24/30 x 100 = 80%. For comparison: Methane (CH4) is 75% C, Benzene (C6H6) is 92.3% C, Cyclohexane (C6H12) is 85.7% C -- only Ethane matches the given 80%.
ग्लुकोज मधे कार्बनची टक्केवारी __________ आहे. / The percentage of carbon in glucose is
The molecular formula of glucose is C6H12O6. Molar mass = (6*12) + (12*1) + (6*16) = 72 + 12 + 96 = 180 g/mol. Percentage of carbon = (72 / 180) * 100 = 40%.